As an integrated management mechanism performing multilayer flow control under a centralized supervisory controller, there is OpenFlow. In the OpenFlow, a packet/field and a rule defining a flow are referred using wildcards to identify the flow, so that it is possible to perform control at a flow level.    [Patent Literature 1] International Publication Pamphlet No. WO 2010/103909 A    [Patent Literature 2] Japanese Laid-open Patent Publication No. 2012-090058 A    [Patent Literature 3] Japanese Laid-open Patent Publication No. 2011-188433 A
However, the flow control described above has a problem in that the number of entries of an Access Control List (ACL) to verify the flow is insufficient.
FIG. 29 is a diagram schematically illustrating a configuration of a network system in the related art.
A network system 5 exemplified in FIG. 29 includes twelve switches 50 and eight server apparatuses 60.
Each server apparatus 60 is communicably connected to the other server apparatuses 60 through one or a plurality of switches 50, and the network system 5 forms a Fat Tree structure. Further, each server apparatus 60 creates a virtual environment 60a. Then, eight Virtual Machines (VMs) 61 are deployed on a memory (not illustrated) provided in each server apparatus 60, and the deployed VMs 61 are executed on a Central Processing Unit (CPU, not illustrated) which is provided in each server apparatus 60.
Herein, assuming that the number of hosts (the server apparatuses 60) in the network is assumed to be h and the number of VMs 61 in each host is assumed to be v, the number of VMs 61 in the network is obtained by h*v=64. Further, the number of flows which are generated on the network is obtained as follows.t=(v*((h−1)*v))*h=h*(h−1)*v*v 
Then, in the network system 5 of h=8 and v=8 as illustrated in FIG. 29, the number of VMs 61 is obtained by h*v=64, and the number of flows is obtained as t=3584 by the above equation.
In other words, 3584 flows are required in communication among 64 VMs 61 at most. A network system under normal operations may include more server apparatuses (VMs) compared to the server apparatuses 60 (VMs 61) illustrated in FIG. 29, and the number of flows is increased further more.
FIG. 30 is a diagram illustrating specifications of switches in the related art.
A rule for defining a flow in the OpenFlow is installed on a Ternary Content Addressable Memory (TCAM) provided in the switch.
However, since the TCAM occupies a large mounting area and consumes a large amount of power, the number of entries of the ACL (the number of flows to be registered) is small.
As exemplified in FIG. 30, switches (device 1 to device 4) in the related art include only about 1 k to 3 k entries of the ACL.
As described above using FIG. 29, the network system 5 including 64 VMs 61 at most requires 3584 flows, and thus the number of entries of the ACL is not sufficient for a commodity switch in the related art. Therefore, there is a problem in that the scale of the network which can be managed using the OpenFlow is restricted.